Highly oriented poly crystalline graphite (HOPG), boron-doped diamond (BDD), nanocrystalline diamond (NCD), ultra-nano-crystalline diamond (uNCD), fullerenes C60 and C70 and Diamond Like Carbon (DLC) surfaces are exposed to low pressure hydrogen plasma in a 13.56 MHz plasma reactor. Relative yields of surface produced Hions due to bombardment of positive ions from the plasma are measured by an energy analyzer cum quadrupole mass spectrometer. Irrespective of plasma conditions (0.2 and 2 Pa), HOPG surfaces show the highest yield at room temperature (RT), while at high temperature (HT), the highest yield (~ 5 times compared to HOPG surface at room temperature) is observed on BDD surfaces. The shapes of ion distribution functions (IDFs) are compared at RT and HT to demonstrate the mechanism of ion generation at the surface. Raman spectroscopy analyses of the plasma exposed samples reveal surface modifications influencing Hproduction yields, while further analyses strongly suggest that the hydrogen content of the material and the sp3/sp2 ratio are the key parameters in driving surface ionization efficiency of carbon materials under the chosen plasma conditions.

A kinetic study is conducted to investigate the elementary processes scheme that produces methane decomposition as a small percentage of this gas is introduced downstream in the flowing afterglow of a nitrogen microwave discharge. For this purpose a self-consistent kinetic model is used for the discharge and corresponding afterglow including, besides the species associated with active nitrogen, such as vibrationally excited molecules, and metastables and N(4S) atoms, various hydrocarbons formed from methane decomposition, and other species produced in nitrogen–methane reactions. It is observed that CH4 is primarily dissociated in CH3 and CH2 in collisions with N2(A), the stable hydrogen cyanide molecule HCN is formed at an intermediate stage of the process, HCN and CH2 give place to the formation of CN(X 2Σ+), and ultimately C atoms are produced by collisions of CN(X) with N atoms. The predicted concentrations so obtained are compared with experimental determinations of N and C atoms and of N2(B 3Πg) and CN(B 2Σ+) states, these latter obtained from spectroscopic measurements.

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